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  1. Apr 12, 2024
    • Adrian Catangiu's avatar
      pallet-xcm: add new extrinsic for asset transfers using explicit XCM transfer types (#3695) · 1e971b8d
      Adrian Catangiu authored
      
      
      # Description
      
      Add `transfer_assets_using()` for transferring assets from local chain
      to destination chain using explicit XCM transfer types such as:
      - `TransferType::LocalReserve`: transfer assets to sovereign account of
      destination chain and forward a notification XCM to `dest` to mint and
      deposit reserve-based assets to `beneficiary`.
      - `TransferType::DestinationReserve`: burn local assets and forward a
      notification to `dest` chain to withdraw the reserve assets from this
      chain's sovereign account and deposit them to `beneficiary`.
      - `TransferType::RemoteReserve(reserve)`: burn local assets, forward XCM
      to `reserve` chain to move reserves from this chain's SA to `dest`
      chain's SA, and forward another XCM to `dest` to mint and deposit
      reserve-based assets to `beneficiary`. Typically the remote `reserve` is
      Asset Hub.
      - `TransferType::Teleport`: burn local assets and forward XCM to `dest`
      chain to mint/teleport assets and deposit them to `beneficiary`.
      
      By default, an asset's reserve is its origin chain. But sometimes we may
      want to explicitly use another chain as reserve (as long as allowed by
      runtime `IsReserve` filter).
      
      This is very helpful for transferring assets with multiple configured
      reserves (such as Asset Hub ForeignAssets), when the transfer strictly
      depends on the used reserve.
      
      E.g. For transferring Foreign Assets over a bridge, Asset Hub must be
      used as the reserve location.
      
      # Example usage scenarios
      
      ## Transfer bridged ethereum ERC20-tokenX between ecosystem parachains.
      
      ERC20-tokenX is registered on AssetHub as a ForeignAsset by the
      Polkadot<>Ethereum bridge (Snowbridge). Its asset_id is something like
      `(parents:2, (GlobalConsensus(Ethereum), Address(tokenX_contract)))`.
      Its _original_ reserve is Ethereum (only we can't use Ethereum as a
      reserve in local transfers); but, since tokenX is also registered on
      AssetHub as a ForeignAsset, we can use AssetHub as a reserve.
      
      With this PR we can transfer tokenX from ParaA to ParaB while using
      AssetHub as a reserve.
      
      ## Transfer AssetHub ForeignAssets between parachains
      
      AssetA created on ParaA but also registered as foreign asset on Asset
      Hub. Can use AssetHub as a reserve.
      
      And all of the above can be done while still controlling transfer type
      for `fees` so mixing assets in same transfer is supported.
      
      # Tests
      
      Added integration tests for showcasing:
      - transferring local (not bridged) assets from parachain over bridge
      using local Asset Hub reserve,
      - transferring foreign assets from parachain to Asset Hub,
      - transferring foreign assets from Asset Hub to parachain,
      - transferring foreign assets from parachain to parachain using local
      Asset Hub reserve.
      
      ---------
      
      Co-authored-by: default avatarBranislav Kontur <[email protected]>
      Co-authored-by: command-bot <>
      1e971b8d